1. Field of the Invention
This invention relates to hyperthermia treatment of living tissues and more particularly to radiation of microwave energy and simultaneous measurement of the temperature at the site of treatment.
2. Description of the Prior Art
Medical practitioners have known that a patient with a cancerous tumor can be successfully treated, by a process which raises the temperature of the tumor. This treatment is generally referred to as hyperthermia. One method of hyperthermia treatment utilizes microwave radiation energy. The temperature of the tissue irradiated by the microwave energy is a function of the power or intensity of the microwave signal applied to the body tissue. The depth of penetration of a microwave signal into the tissue is, in general, an inverse function of the signal frequency employed. The volume of the tissue to be treated is controlled by the electrical and geometrical design of the microwave applicator.
The microwave radiation may be controlled to elevate the temperature of a known volume of tissue. During microwave radiation, it is desirable to prevent overheating of the tissue as well as the surrounding tissues. It is correspondingly desirable to provide an accurate measurement of the temperature of the tissue being treated, particularly at the site of the tumor. Prior methods for measuring the temperature of the treated tissue employ thermocouples, thermometers or radiometers. One such method utilizing a radiometer is described in U.S. Pat. application, Ser. No. 808,272, filed on June 20, 1977 entitled "Apparatus for Hyperthermia Treatment" by Fred Sterzer.
Thermocouples for measuring the temperature of the treated tissue may be either attached to the surface of the skin or invasively positioned beneath the skin at or near the site of the tumor to be treated. Thermocouples are used while measuring temperature during treatment to switch off the microwave radiation to the tissue upon sensing a predetermined temperature. However, thermocouples positioned near or in close proximity to the irradiating signal distort the applied microwave signal inducing anomalous heating effects which contribute to inaccurate temperature control. It is known to measure the tissue temperature with a thermocouple only at a time when the irradiation signals are removed. Such an arrangement is described in the above-identified U.S. Pat. application, Ser. No. 840,036.
It is further known to utilize a thermometer disposed within a radio frequency radiating electrode to measure the temperature within the electrode, as described in U.S. Pat. No. 2,126,257, entitled "Electromedical Instrument," issued Aug. 9, 1938, to Frank E. Hird.